Bone anchoring device and tool cooperating with such a bone anchoring device

ABSTRACT

A bone anchoring device includes a receiving part including a rod receiving portion with a first end, a second end, and a U-shaped recess for receiving a rod, the recess defining two free legs, and a head receiving portion at the second end for introducing and clamping the head, and a locking ring configured to be arranged around the head receiving portion, the locking ring including an engagement structure for engagement with a tool, the engagement structure defining a width of the locking ring that is greater than a greatest width of the rod receiving portion, wherein the locking ring can assume a locking position exerting a greatest compressive force on the head receiving portion of the receiving part to lock an inserted head, and wherein the locking ring is movable out of the locking position towards the first end of the rod receiving portion.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.13/631,503, filed Sep. 28, 2012, which claims priority to and thebenefit of U.S. Provisional Patent Application Ser. No. 61/541,511,filed Sep. 30, 2011, the contents of which are hereby incorporated byreference in their entirety. This application also claims priority toand the benefit of European Patent Application No. EP 11 183 616.9,filed Sep. 30, 2011, the contents of which are hereby incorporated byreference in their entirety.

BACKGROUND

1. Field of the Invention

The invention relates to a bone anchoring device including a boneanchoring element and a receiving part for coupling a rod to the boneanchoring element. The receiving part includes a rod receiving portionfor receiving the rod and a head receiving portion that is flexible soas to allow introduction and clamping of a head of the bone anchoringelement. The bone anchoring device further includes a locking ringarranged around the head receiving portion that can assume a lockingposition in which an inserted head is locked by compression of the headreceiving portion of the receiving part. The locking ring has an outersurface with an engagement portion for engagement with a tool. The toolis configured to cooperate with the receiving part and the locking ringso as to allow releasing of the locking ring from a position in whichthe locking ring locks the head. The bone anchoring device can berealized, for example, in the form of a polyaxial bone screw.

2. Description of Related Art

US 2009/0149887 A1 discloses an apparatus for connecting a bone anchorto a support rod, the apparatus including a connector body and a cap.The connector body has a socket for insertion, angulation and removal ofa bone anchor. A sleeve is provided, which is configured to fit over theconnector body in a temporary position, in which the sleeve permitsinsertion of the bone anchor, to move to a provisional locking position,in which the sleeve permits angulation but prevents removal of the boneanchor, and to move to a locking position in which the sleeve preventsboth angulation and removal of the bone anchor. Tools are provided forinstalling the connector body, the sleeve, a cap and the support rod.

SUMMARY

It is an object of the invention to provide a bone anchoring device thatmakes use of an outer locking ring for compressing a head receivingportion to lock a head of a bone anchoring element therein, that isimproved with respect to its handling. Further, a tool can be providedthat allows or facilitates such improved handling.

The bone anchoring device according to embodiments of the inventionprovide for safer loosening of a locking mechanism of the device. Also,the bone anchoring device according to embodiments of the inventionenables a surgeon or other practioner to carry out revisions or furtherpositioning or repositioning of the angular positioning of a receivingpart with respect to the bone anchoring element. In one embodiment, areleasing of the locking mechanism may be possible with a rod stillinserted.

The tool according to embodiments of the invention is configured toengage the receiving part and to be operated along a central axis of thereceiving part. Therefore, it will not be necessary to have additionalspace for laterally applying the tool. Furthermore, the tool will not bejammed by, for example, forces acting only from one side.

Therefore, handling of the bone anchoring device can be simplified,because once a locking of the head is achieved, such locking can bereleased without applying larger forces that could result in damage tosurrounding material, such as tissue, blood vessels, or nerves.Revisions or secondary adjustments of the rod and the receiving part canthus be performed in a more controlled manner.

With the bone anchoring device according to embodiments of theinvention, a modular system can be provided that allows for combining ofvarious anchoring elements with any suitable receiving part on demand,depending on the actual clinical requirements. This reduces the overallcosts of using polyaxial screws, reduces inventory, and gives thesurgeon a wider or more versatile choice of implants.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows a perspective exploded view of a first embodiment of a boneanchoring device;

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state;

FIG. 3 shows an enlarged side view of the bone anchoring device of FIGS.1 and 2 in the assembled state;

FIG. 4 shows a cross-sectional view of the bone anchoring device shownin FIG. 3, the section being taken perpendicular to an axis of aninserted rod;

FIG. 5 shows a perspective view of a receiving part according to anembodiment of the invention;

FIG. 6 shows a cross-sectional view of the receiving part of FIG. 5, thesection taken perpendicular to an axis of a channel for receiving a rod;

FIG. 7 shows a top view of the receiving part of FIG. 5;

FIG. 8 shows a perspective view of a locking ring of the bone anchoringdevice according to the first embodiment;

FIG. 9 shows a cross-sectional view of the locking ring of FIG. 8, thesection taken perpendicular to an axis of a connected rod;

FIG. 10 shows a top view of the locking ring of FIG. 8;

FIG. 11 shows a perspective exploded view of an embodiment of a toolthat cooperates with the bone anchoring device according to the firstembodiment;

FIG. 12 shows a cross-sectional view of the tool of FIG. 11 in anenlarged view, the section taken through a central axis andperpendicular to a long side of a handle portion of the tool;

FIG. 13 shows a perspective view of a first step of mounting the tool ofFIGS. 11 and 12 to the bone anchoring device of FIGS. 1 and 2;

FIG. 14 shows a cross-sectional view of a further step of mounting thetool of FIGS. 11 and 12 to the bone anchoring device according to thefirst embodiment;

FIG. 15 shows a perspective view of a further step of mounting the toolof FIGS. 11 and 12;

FIG. 16 shows an enlarged cross-sectional view of a portion of the toolattached to the bone anchoring device shown in FIG. 15;

FIG. 17 shows a perspective view of a further step of mounting the toolof FIGS. 11 and 12 to the bone anchoring device of FIGS. 1 and 2;

FIG. 18 shows an enlarged cross-sectional view of a portion of the toolmounted to the bone anchoring device as shown in FIG. 17;

FIG. 19 shows a further enlarged portion of FIG. 18;

FIG. 20 shows a perspective view of a first step of releasing a lockingmechanism of the bone anchoring device of FIGS. 1 and 2 with the tool ofFIGS. 11 and 12;

FIG. 21 shows an enlarged cross-sectional view of the tool and boneanchoring device shown in FIG. 20;

FIG. 22 shows an enlarged portion of FIG. 21;

FIG. 23 shows a perspective view of a step of removing the tool of FIGS.11 and 12 from the bone anchoring device of FIGS. 1 and 2;

FIG. 24 shows an enlarged cross-sectional view of a portion of the tooland bone anchoring device shown in FIG. 23;

FIG. 25 shows a perspective view of a bone anchoring device according toa second embodiment in an assembled state;

FIG. 26 shows a side view of a locking ring of the bone anchoring deviceaccording to the second embodiment shown in FIG. 25;

FIG. 27 shows a top view of the locking ring of FIG. 26;

FIG. 28 shows a cross-sectional view of the locking ring of FIG. 26;

FIG. 29 shows a side view of the tool according to a second embodiment;

FIG. 30 shows a cross-sectional view of the tool of FIG. 29, the sectiontaken along a central axis and perpendicular to a long side of a handleportion of the tool;

FIG. 31 shows a perspective view of a first step of mounting the tool tothe bone anchoring device according to the second embodiment;

FIG. 32 shows a perspective view of a next step of mounting the tool tothe bone anchoring device according to the second embodiment;

FIG. 33 shows a further step during the procedure of mounting the toolto the bone anchoring device according to the second embodiment;

FIG. 34 shows a perspective view of a next step of mounting according tothe second embodiment, wherein ribs at the locking ring are engaged bythe tool;

FIG. 35 shows a cross-sectional view of the bone anchoring device withthe tool mounted thereon according to the second embodiment;

FIG. 36 shows an enlarged cross-sectional view of the device of FIG. 35rotated by about 45°;

FIG. 37 shows an enlarged portion of FIG. 36; and

FIG. 38 shows a cross-sectional view of the bone anchoring device in astep of removing or detaching the tool according to the secondembodiment.

DETAILED DESCRIPTION

As shown in FIGS. 1 and 2, a bone anchoring device according to anembodiment of the invention includes a bone anchoring element 1 in theform of, for example, a bone screw having a shank 2 with a threadedportion and a head 3 with a spherically-shaped outer surface portion.The head 3 has a recess 4 for engagement with a driver or tool. The boneanchoring device also includes a receiving part 5 for receiving a rod 6to be connected to the bone anchoring element 1. Further, a fixationelement 7 in the form of, for example, an inner screw may be providedfor fixing the rod 6 in the receiving part 5. The bone anchoring devicefurther includes a locking ring 8 for locking the head 3 in thereceiving part 5.

Referring to FIGS. 1 to 7, the receiving part 5 includes a rod receivingportion 9 which may have a portion that is substantially cylindrical.The rod receiving portion 9 has a first end 9 a and an opposite secondend 9 b, and a central axis C that passes through the first end 9 a andthe second end 9 b. A coaxial first bore 10 is provided at the secondend 9 b as shown, for example, in FIGS. 6 and 7. A diameter of the firstbore 10 is smaller than a diameter of the head 3 of the bone anchoringelement 1. The rod receiving portion 9 further includes a coaxial secondbore 11 extending from the first end 9 a to a distance from the secondend 9 b. A diameter of the second bore 11 is larger than the diameter ofthe first bore 10. By the second bore 11, an abutment surface 11 a isprovided or formed inside the rod receiving portion 9 that may serve asan abutment for a tool, to be described in more detail below. Asubstantially U-shaped recess 12 extends from the first end 9 a in thedirection of the second end 9 b in the rod receiving portion 9, whereina width of the recess 12 is slightly larger than a diameter of the rod6, in such a way that the rod 6 can be placed in the recess 12 and canbe guided therein. By means of the recess 12, two free legs 12 a, 12 bare formed, on which an internal thread 13 may be provided. The internalthread 13 can be, for example, a metric thread, a flat thread, anegative angle-thread, a saw-tooth thread, or any other thread form.Preferably, a thread form such as a flat thread or a negative anglethread that prevents or reduces splaying of the legs 12 a, 12 b when theinner screw 7 is screwed-in is used. A depth of the recess 12, whichforms a channel for the rod 6, is such that the rod 6 and the innerscrew 7 can be inserted between the legs 12 a, 12 b. Cut-outs 15 areprovided in the rod receiving portion 9, extending from the second end 9b to the recess 12. The cut-outs 15 are provided on either end of thechannel formed by the recess 12.

The inner screw 7 has a thread corresponding to the internal thread 13provided on the legs 12 a, 12 b. If a thread form that prevents the legsfrom splaying is used, a single locking element such as the inner screw7 may be sufficient.

On an outer surface of the rod receiving portion 9, in the region of thelegs 12 a, 12 b, a groove 16 may be provided that extends in acircumferential direction and serves for engagement with a portion ofthe locking ring 8. The groove 16 may be asymmetric in such a way toallow for disengagement of the locking ring 8 and the groove 16 when thelocking ring 8 is shifted downwards, away from the second end 9 b.

At the side of the second end 9 b, the receiving part 5 further includesa head receiving portion 17 providing an accommodation space for thehead 3 of the bone anchoring element 1. The head receiving portion 17has a greatest outer diameter that is smaller than a greatest outerdiameter of the rod receiving portion 9. An internal hollow section 18forms a seat for the head 3 of the bone anchoring element 1, and is openvia an opening 19 to a free end 17 b of the head receiving portion 17.The internal hollow section 18 is adapted in its shape to the shape ofthe head 3. In the embodiment shown, section 18 is a spherical sectionto accommodate spherical head 3. Furthermore, the hollow section 18 isconfigured to encompass the head 3 of the bone anchoring element 1 fromthe side, to cover a region including a largest diameter of the head 3.

A plurality of slits 20 are provided in the head receiving portion 17that are open to the free end 17 b. The slits 20 render the headreceiving portion 17 flexible so that the head receiving portion 17 canbe compressed to clamp and finally lock an inserted head 3 in the hollowinternal portion 18 by means of friction. A number and size of the slits20 is provided depending on the desired flexibility of the headreceiving portion 17. The flexibility of the head receiving portion 17is such that the head 3 of the bone anchoring element 1 can be insertedby expanding the head receiving portion 17, and can be clamped bycompressing the head receiving portion 17.

An outer surface of the head receiving portion 17 has a first section 21with an outer diameter increasing towards the free end 17 b, forexample, in an outwardly curved or conically widening manner. Adjacentto the first section 21, there may be a circumferential groove 22 thatis recessed with respect to the first section 21 and that serves forengagement with a portion of the locking ring 8. The groove 22 may beshaped so as to allow for disengagement of the locking ring 8 and thegroove 22 when moving the locking ring 8 in a direction towards the freeend 17 b (or away from the first end 9 a of the rod receiving portion).This is realized, for example, by having a lower wall of the groove 22that is inclined towards the free end 17 b.

Adjacent the groove 22, there is a third portion 23 of the headreceiving portion 17 with a substantially cylindrical outer surface. Thethird portion 23 may be configured to cooperate with a portion of thelocking ring 8 to enhance a clamping effect of the locking ring 8.

The locking ring 8 will now be described in particular with reference toFIGS. 3, 4, and 8 to 10. The locking ring 8 may include a portion thatis substantially cylindrical, and has an upper end 8 a and a lower end 8b. In a mounted state, the upper end 8 a is oriented in the direction ofthe first end 9 a of the rod receiving portion 9 and the lower end 8 bis oriented in the direction of the free end 17 b of the head receivingportion 17. Approximately in a central region of the locking ring 8, atan inner wall, a first portion 81 is provided that cooperates with thefirst outer surface portion 21 of the head receiving portion 17 tocompress the head receiving portion 17. The first portion 81 may beslightly tapered, may be straight, or may be curved with a curvaturedirected towards a center of the locking ring 8. Furthermore, at thelower end 8 b, the locking ring has an inwardly projecting edge 82, aninner diameter of which is smaller than inner diameters of otherportions of the locking ring 8. The inwardly projecting edge 82 isconfigured to engage the groove 22 of the head receiving portion 17 andto finally engage the cylindrical portion 23 of the head receivingportion 17 when the bone anchoring device is in a locked state.

The locking ring 8 also has a third portion including upwardly extendingwall portions 83 a that are separated from each other by slits 84. Theupwardly extending wall portions 83 a are arranged at an outercircumference of an inner circumferential shoulder 85 of the lockingring 8, and render the third portion of the locking ring 8 flexible. Anumber and size of the slits 84 and a thickness of the wall portions 83a are configured such that a desired flexibility is obtained. Atrespective free ends of the wall portions 83 a, the wall portions 83 aare configured to engage the groove 16 provided on the outer surface ofthe rod receiving portion 9.

Two projections 86 that are located diametrically opposite to each otherare also formed in the third portion of the locking ring 8. Theprojections 86 have such a height that they extend through the cut-outs15 and project above a bottom of the substantially U-shaped recess 12when the locking ring 8 is in a position where its shoulder 85 abuts thesecond end 9 b of the rod receiving portion 9. A free end surface 86 aof the projections 86 may be curved, for example, concave. The lockingring 8 is arranged around the head receiving portion 17 of the receivingpart 5 such that the projections 86 are located at the positions of therecess 12. By means of this, the projections 86 prevent the locking ring8 from rotating relative to the receiving part 5 when the rod 6 is notyet inserted.

The locking ring further includes on its outer surface portion adjacentthe upwardly extending wall portions 83 a an engagement portion 88 forengagement with a tool, described in more detail below. In a firstembodiment, the engagement portion 88 is realized by an external thread.The thread extends in an axial direction of the locking ring 8 along aportion of the outer surface of the locking ring 8. A depth of thethread may be small, so that a violation of surrounding tissue or bloodvessels can be avoided or minimized. Aligned with and just below theprojections 86, the thread may be interrupted at two oppositethread-free sections 89. The thread may be, for example, flattenedtowards the center at the thread-free sections 89, respectively. Thesections 89 may serve for applying a distraction or compression tool.The thread-free sections 89 can also be provided at other positions, orin some embodiments, more than two thread-free sections 89 can beprovided.

The receiving part 5, the locking ring 8, the inner screw 7, and thebone anchoring element 1 may be made of bio-compatible materials, forexample, of titanium or stainless steel, of a bio-compatible alloy suchas Nitinol, or of a bio-compatible plastic material, such as PEEK(Polyetheretherketone). The parts can be made of the same or ofdifferent materials.

In an embodiment of the invention, the locking ring 8 can assume threemain positions relative to the receiving part 5. In a first position(not shown), the inwardly projecting edge 82 of the locking ring 8engages or is positioned adjacent to the groove 22 of the head receivingportion 17. In this position, the head 3 of the bone anchoring element 1can be introduced into the internal hollow space 18 from the free end 17b of the head receiving portion 17. The locking ring 8 is prevented frommoving further upwards towards the first end 9 a of the rod receivingportion 9 because the shoulder 85 abuts against the second end 9 b ofthe rod receiving portion 9.

In a second position, the locking ring 8 is shifted towards the free end17 b of the head receiving portion 17 until the flexible wall sections83 a snap with their free ends into the groove 16 of the rod receivingportion 9. In this position, the head 3 is not yet locked, but may beprevented from removal out of the internal hollow space 18. The head 3may also be frictionally clamped in this state to such an extent thatthe bone anchoring element 1 is still movable relative to the receivingpart 5 when a force, for example, a manually applied force, is appliedto overcome the friction force. An example of the second position can beseen, for example, in FIGS. 21 and 22.

In a third position, the locking ring 8 is shifted further towards thefree end 17 b of the head receiving portion 17 (or away from the firstend 9 a of the rod receiving portion 9) such that the head 3 is finallylocked. In this position, the head receiving portion 17 is compressed bythe locking ring 8, so that the head 3 cannot move and is fixed at anangular position with respect to the receiving part 5. Between upperends of the flexible wall sections 83 a and an upper wall of the groove16 of the rod receiving portion 9 is a gap 90, as shown, for example, inFIG. 4. In the locked condition of the head 3, the locking ring 8 cannotbe loosened, or may be very difficult to loosen, under normal operatingconditions.

A tool 50 according to a first embodiment will now be described withreference to FIGS. 11 and 12.

The tool 50 includes a tubular member 51 with a front end 52 and a rearend 53 opposite to the front end 52. Adjacent the front end 52, thetubular member 51 has at its inner wall an engagement portion 54 forengaging the engagement portion 88 of the locking ring 8. An innerdiameter of the tubular member 51 at the front end 52 is therefore suchthat the tubular member 51 can be placed onto or around the receivingpart 5 and can engage the locking ring 8. At a distance from the frontend 52 a stop 55 is provided within the tubular member 51 that abutsagainst the upper edge 8 a of the locking ring 8 when the engagementportion 54 engages the threaded portion 88, for example, as shown inFIG. 14. At its rear end 53, the tubular member 51 also has an internalthreaded portion 56.

The tool 50 further includes a shaft 60 with a front end 61 and a rearend 62 that can be formed as a handle. The shaft 60 has an outerthreaded portion 63 at a distance from the handle that cooperates withthe internal threaded portion 56 of the tubular member 51. Adjacent theouter threaded surface portion 63 is a stop 64 that limits the insertiondepth of the shaft 60 into the tubular member 51. The stop 64 can be,for example, a circumferential shoulder. The shaft 60 is insertable intothe tubular member 51 and is movable therein. An insertion depth can beadjusted by the cooperation of the threads 56 and 63 of the tubularmember 51 and the shaft 60, respectively. As shown in FIG. 12, when theshaft 60 is inserted and screwed into the tubular member 51 until thestop 64 abuts against the rear end 53, the front end 61 of the shaft 60is at a distance from the front end 52 of the tubular member 51.

The shaft 60 has at its front end 61 a blind hole 65, in which a post 66can be supported by a spring 67. An end surface 66 a of the post 66projects out of the front end 61 of the shaft (see, e.g., FIG. 16) andthe post 66 is movable in the blind hole 65. The movement of the post 66in the blind hole 65 may be limited in two directions by a stop. Thestop may be formed by an axially elongated hole 68 that extends throughthe post 66 and through which a pin 69 is passed. The pin 69 extendsthrough a transverse hole 70 provided in the shaft 60, as shown inparticular in FIG. 11. By means of this, the post 66 is moveable betweena first position in which the pin is at an end of the elongate hole 68nearer to the spring 67, to a second position in which the pin 69 is atan end of the elongate hole 68 nearer to the front end 61 of the shaft60. In the first position, the post 66 projects further outward from thefront end 61 and may be biased by partial compression of the spring 67.In the second position, the post 66 is urged towards the end of theblind hole 65, thereby further compressing the spring 67. The spring 67is shown as a helical spring, but can be any other spring or mechanismthat accomplishes the same purpose. For example, the spring mechanismcan also be realized by an elastomer cushion.

Operation of the tool 50 will now be described with reference to FIGS.13 to 24. First, the tubular member 51 may be separated from the shaft60. As shown in FIGS. 13 and 14, the tubular member 51 is placed overthe receiving part 5 (of a locked bone anchoring device, for example)until the threaded portion 54 engages the threaded portion 88 of thelocking ring 8.

In a next step, shown in FIGS. 15 and 16, the shaft 60 is inserted intothe tubular member 51 until the front end 66 a of the post 66 abutsagainst the abutment surface 11 a in the receiving part 5 (see FIG. 16).In this position, the front end 61 of the shaft 60 is spaced apart fromthe first end 9 a of the rod receiving portion 9 of the receiving part5. The post 66 is in its first position, where the pin 69 is nearer tothe spring 67. The shaft 60 is not yet fully introduced into the tubularmember 51. As shown in FIGS. 17 and 18, the shaft 60 is thereafterfurther screwed into the tubular member 51 until the front end 61 of theshaft abuts against the first end 9 a of the rod receiving portion 9 ofthe receiving part 5. Thereby, a counterforce acting onto the post 66presses the post 66 into the blind hole 65 against the force of thespring 67. In this condition, the locking ring 8 is still in its thirdposition, in which the head is locked. This can be seen more clearly inthe enlarged representation according to FIG. 19 that shows the gap 90between the upper end 8 a of the locking ring 8 and the wall of thegroove 16 facing the upper end 8 a.

For releasing the locking ring 8 from the locking position, the tubularmember 51 can be gripped at a gripping portion 57 and held in thisposition while the shaft 60 is further screwed into the tubular member51, as shown in FIG. 21. By means of this, the locking ring 8 is drawnupwards (i.e., towards first end 9 a of rod receiving portion 9) untilflexible wall section 83 a abuts the upper wall of groove 16, as shownin detail in FIG. 22. Here, the locking ring 8 is in the secondposition, where the locking ring 8 does not lock the head 3.

A step of removing the tool is shown in FIGS. 23 and 24. The handle atend 62 can be turned in the other or opposite direction. The lockingring 8 abuts against an end of the groove 16, as shown in FIG. 22, andtherefore, it can not be drawn further upwards (e.g., back towards theinsertion position). Because the post 66 abuts against the abutmentsurface 11 a of the receiving part, the screwing back of the shaft 60does not result in simultaneous rotation of the receiving part 5 and thelocking ring 8. Hence, the tool 50 can be removed easily. Then, theangular position between the bone anchoring element 1 and the receivingpart 5 can be readjusted.

A second embodiment of the bone anchoring device is shown in FIGS. 25 to28. The second embodiment differs from the bone anchoring deviceaccording to the first embodiment by the design of an engagement portionof the locking ring 8′. All other parts are identical or similar to thefirst embodiment and are marked with the same reference numerals. Thedescription of the same or similar parts is not repeated.

The locking ring 8′ has an engagement portion for a tool that is in theform of diametrically opposite rib portions that extendcircumferentially. In the embodiment shown, two rib portions 88 a′ and88 b′ are arranged at an outer surface of the locking ring 8′ beneaththe elastically deformable wall portions 83 a. The rib portions 88 a′,88 b′ extend over a segment of an outer circumference of the lockingring 8′ for approximately a quarter circle or less than a quartercircle. The rib portions 88 a′, 88 b′ may be arranged at an angle ofapproximately 45° with respect to the projections 86 that support therod 6 around a circumference of the locking ring 8′.

Each rib portion 88 a′, 88 b′ includes two circumferentially extendingribs 881 a′, 882 a′ and 881 b′, 882 b′, respectively, that are spacedfrom each other in an axial direction of the locking ring 8′. The ribs881 a′, 882 a′, 881 b′, 882 b′ may be slightly inclined towards thesecond end 8 b of the locking ring 8′, as can be seen in particular inFIG. 28. The downward inclination of the ribs 881 a′, 882 a′, 881W, 882Wprovide an undercut for engagement with the tool described below thatenhances the safety of the engagement with the tool. In the embodimentshown, two ribs in each rib portion 88 a′, 88 b′ are provided. It shallbe noted, however, that one rib for each rib portion may be sufficient.Also, more than two ribs can be provided for each rib portion.

A tool for releasing the locking ring from a locked portion according toa second embodiment will be described, referring to FIGS. 29 and 30. Thetool 50′ includes a tubular member 51′ with two substantiallyrectangular recesses 51 a′, 51 b′ at a front end 52′. Adjacent the frontend 52′, engagement portions 54 a′, 54 b′ that correspond to andcooperate with the rib portions 88 a′, 88 b′ are located inside thetubular member 51′. The engagement portions 54 a′, 54 b′ are ribportions with an inclination or bias away from the front end 52′. At adistance from the front end 52′, a stop 55′ is provided. Thesubstantially rectangular recesses 51 a′, 51 b′ have a size that may beapproximately a size of rib-free portions of the locking ring in acircumferential direction, and have a depth in an axial direction thatis such that when the tubular member 51′ is placed onto the receivingportion and engages the locking ring 8′, an inserted rod 6 can passthrough the recesses 51 a′ 51 b′.

The tubular member 51′ also has a rear end 53′ with an internallythreaded portion 56′. At or in a vicinity of the rear end 53′, a gripportion 57′ is provided for facilitating gripping.

The tool 50′ further includes a shaft portion 60′ with a front end 61′and a rear end 62′ that is provided with a handle. At a distance fromthe rear end 62′, an externally threaded portion 63′ is provided thatcooperates with the internally threaded portion 56′ of the tubularmember 51′, similarly as seen in the first embodiment. Furthermore,similar to the first embodiment, a stop in form of an annular shoulder64′ may be provided at a distance from the rear end 62′. The shaft 60′in this embodiment may not have a resiliently supported post as seen inthe previous embodiment. A length of the shaft portion 60′ is such thatwhen the shaft portion 60′ is inserted and screwed into the tubularmember 51′ until the stop 64′ abuts against the rear end 53′ of thetubular member 51′, the recesses 51 a′, 51 b′ at the front end 52′ cancover or accommodate the receiving part 5 and the rod 6 insertedtherein.

The tool 50′ according to the second embodiment can be applied, forexample, when the rod 6 is inserted and the inner screw 7 is removed. Asshown in FIG. 31, the tool 50′ is oriented such that the engagementportion in the form of the ribs 54 a′, 54 b′ is placed at or alignedwith the rib-free portions of the locking ring 8′. The rod 6 may abutagainst one side of the recesses 51 a′, 51 b′. The tubular member 51′ isshifted downwards until the stop 55′ abuts against the upper edge 8 a ofthe locking ring 8′. Thereafter, as shown in FIGS. 32 to 34, the tubularmember 51′ is rotated so that the engagement portions 54 a′, 54 b′inside the tubular member 51′ engage the rib portions 88 a′, 88 b′ onthe outer surface of the locking ring 8′. Because the recesses 51 a′, 51b′ are sufficiently large in a circumferential direction, the tubularmember 51′ can be rotated such that the rod 6 may abut against the otherside of the recesses 51 a′, 51 b′ after rotation, as shown in FIG. 34.

Thereafter, as shown in FIGS. 35 to 37, the shaft 60′ is screwed furtherinto the tubular member 51′ until its front end 61′ abuts against thefirst end 9 a of the rod receiving portion 9 of the receiving part 5. Ina next step, as shown in FIG. 38, the shaft 60′ is further moved intothe tubular member 51′ while the tubular member 51′ is held at thegripping portion 57′, for example, by a practitioner. By means of this,the locking ring 8′ is pressed upwards (i.e. towards the first end 9 aof the rod receiving portion 9) and is released from the lockingposition.

For the removal of the tool 50′, the shaft 60′ is slightly screwed back,then the tubular member 51′ is rotated until the engagement portions 54a′, 54 b′ of the tubular member no longer engage the engagement portions88 a′, 88 b′ at the locking ring 8′. The tool 50′ can then be removed bypulling the tool 50′ upwards, away from the bone anchoring device.

It shall be noted that further modifications of the embodiments shownare also possible. For example, the tool according to the secondembodiment may also include a post that is supported by a spring. Also,the tool according to the second embodiment may have a threadedengagement portion for engaging a threaded locking ring, similar to thefirst embodiment. The tool of the first embodiment may also be providedwithout a post.

For the engagement at the locking ring, other modifications are alsoconceivable. For example, it may be possible to have engagement portionswith various other shapes.

The bone anchoring device according to other embodiments of theinvention can be provided in a modified form. For example, the head ofthe bone anchoring element can have any other shape, such as, forexample, a cylindrical shape, whereby a monoaxial bone screw isprovided, allowing for rotation of a screw element with respect to thereceiving part around a single axis. The head can also be conicallyshaped or otherwise shaped, with the internal hollow section of the headreceiving portion adapted to the shape. In a further modification,flexibility of the head receiving portion may be based on or facilitatedby properties of the material, for example, a plastic material may beused, and the slits may be fully or partly omitted.

The projections of the locking ring that engage the rod can also havevarious other shapes. The surface of the free end can be flat or can beotherwise shaped. The projections can be also omitted.

The head receiving portion can have an inclined open end or can beotherwise asymmetric to allow for a greater angulation of an insertedhead in one direction.

The outer surface of the head receiving portion and the inner surface ofthe locking ring can also have other shapes that allow a compression ofthe locking ring by means of an increasing force when the locking ringis shifted downward.

The locking ring can also have various other designs. For example, thelocking ring can be formed without the flexible wall sections.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

1. A bone anchoring device comprising: a receiving part for coupling arod to a bone anchoring element, the receiving part comprising: a rodreceiving portion with a first end, a second end, and a U-shaped recessfor receiving a rod, the recess extending from the first end in adirection of the second end and defining two free legs; and a headreceiving portion at the second end for accommodating a head of a boneanchoring element, the head receiving portion having a free end andbeing flexible for introducing and clamping the head; and a locking ringconfigured to be arranged around the head receiving portion, the lockingring comprising an engagement structure for engagement with a tool;wherein when the locking ring is around the head receiving portion, thelocking ring can assume a locking position where the locking ring exertsa greatest compressive force on the head receiving portion of thereceiving part to lock an inserted head; and wherein the locking ring ismovable out of the locking position towards the first end of the rodreceiving portion.
 2. The bone anchoring device, of claim 1, wherein theengagement structure comprises a plurality of ribs extending in acircumferential direction of the locking ring.
 3. The bone anchoringdevice of claim 2, wherein the ribs do not extend around an entirecircumference of the locking ring.
 4. The bone anchoring device of claim1, wherein the engagement structure comprises at least two ribs spacedapart from each other in an axial direction of the locking ring.
 5. Thebone anchoring device of claim 1, wherein the engagement structurecomprises a thread.
 6. The bone anchoring device of claim 1, wherein thelocking ring comprises two projections that are 180° offset from eachother for engagement with a rod.
 7. The bone anchoring device of claim6, wherein the engagement structures are spaced apart in acircumferential direction of the locking ring and grouped into twogroups to the left and right of the projections.
 8. The bone anchoringdevice of claim 7, wherein each of the groups is arranged closer to acorresponding one of the projections.
 9. The bone anchoring device ofclaim 1, wherein the head receiving portion has an exterior surface witha tapered or curved portion and the locking ring has an interior surfacewith a tapered or curved portion which are configured to cooperate withone another, such that an inserted head is clamped when the locking ringis moved towards the free end.
 10. The bone anchoring device of claim 1,further comprising a bone anchoring element having a shank for anchoringin a bone and a head.
 11. A tool for a bone anchoring device comprisinga bone anchoring element having a shank and a head, a receiving partcomprising a rod receiving portion with a first end, a second end, and aU-shaped recess for receiving a rod, the recess extending from the firstend in a direction of the second end and defining two free legs, a headreceiving portion at the second end accommodating the head of the boneanchoring element, the head receiving portion having a free end andbeing flexible for introducing and clamping the head, and a locking ringaround the head receiving portion, the locking ring comprising anengagement structure, wherein the locking ring can assume a lockingposition where the locking ring compresses the head receiving portion ofthe receiving part to lock the head, the tool configured to move thelocking ring out of the locking position towards the first end of therod receiving portion, the tool comprising: a tubular member having afirst end, a second end, and an engagement portion at an inner wall ofthe first end for engaging the engagement structure of the locking ring;and a shaft insertable into the tubular member and movable relative tothe tubular member in an axial direction, the shaft having a first end;wherein when the locking ring is in the locking position and the head islocked relative to the receiving part and the engagement portion of thetubular member engages the engagement structure of the locking ring, thefirst end of the shaft abuts against the rod receiving portion of thereceiving part, such that the shaft is configured to move relative tothe tubular member to move the locking ring out of the locking positiontowards the first end of the rod receiving portion to release thelocking of the head.
 12. The tool of claim 11, wherein the first end ofthe shaft has a coaxial bore, wherein a post provided within the bore ofthe shaft is configured to extend out of the bore of the shaft and to bemovable relative to the shaft.
 13. The tool of claim 12, wherein thepost is elastically supported relative to the shaft.
 14. The tool ofclaim 12, wherein movement of the post relative to the shaft is limitedby at least one stop.
 15. The tool of claim 12, wherein the post isconfigured to abut against a portion of the receiving part differentfrom a portion of the receiving part the first end of the shaft isconfigured to abut against.
 16. The tool of claim 11, wherein tworecesses located opposite to each other are provided at the first end ofthe tubular member to facilitate engagement of the tool with a boneanchoring device with an inserted rod, such that the inserted rod isconfigured to pass through the two recesses of the tubular member. 17.The tool of claim 16, wherein the recesses are substantially rectangularand have a width configured to allow rotation of the tubular memberabout the bone anchoring device with the inserted rod, to facilitate theengagement of the engagement portion with the engagement structure. 18.The tool of claim 16, wherein an abutment is provided at a distance fromthe first end of the tubular member for abutting against a portion ofthe locking ring spaced apart from the engagement structure. 19-20.(canceled)
 21. A method of unlocking a bone anchoring device from alocked position, the bone anchoring device comprising a bone anchoringelement having a shank and a head, a receiving part comprising a rodreceiving portion with a first end, a second end, and a U-shaped recessfor receiving a rod, the recess extending from the first end in adirection of the second end and defining two free legs, a head receivingportion at the second end accommodating the head of the bone anchoringelement, the head receiving portion having a free end and being flexiblefor introducing and clamping the head, and a locking ring around thehead receiving portion, the locking ring comprising an engagementstructure, wherein when the locking ring is in the locked position, thelocking ring compresses the head receiving portion of the receiving partand locks the head, the method comprising: attaching a tool to the boneanchoring element, the tool comprising a tubular member having a firstend, a second end, and an engagement portion at an inner wall of thefirst end, and a shaft in the tubular member and movable relative to thetubular member in an axial direction, the shaft having a first end, theattaching comprising engaging an engagement portion at an inner wall ofthe first end of the tubular member to the engagement structure of thelocking ring, such that the first end of the shaft abuts against the rodreceiving portion of the receiving part; and moving the shaft relativeto the tubular member to move the locking ring out of the lockingposition towards the first end of the rod receiving portion to releasethe locking of the head. 22-23. (canceled)
 24. The method of claim 21,wherein the first end of the tubular member of the tool has two recessesconfigured to allow attachment of the tool to the bone anchoring devicewhen a rod is inserted in the U-shaped recess.